The mean body mass index (BMI) for boys age 12 is 23.6. an investigator wants to test if the BMI is higher in boys age 12 living in new york city. How many boys are needed to ensure that a two-sided test of hypothesis has 80% power to detect an increase in BMI of 2 units? Assume that the standard deviation in BMI is 5.7.
An investigator wants to design a study to estimate the difference in the mean BMI between boys and girls age 12 living in new york city. How many boys and girls are needed to ensure 95% confidence interval estimate for the difference in mean BMI between boys and girls has a margin of error not exceeding 2 units?